Circuit and method for digital delay and circuits incorporating the same

Abstract

A method includes generating multiple delayed versions of a first signal using at least one first delay line, selecting at least one version of the first signal, and generating a second signal based on the first signal and the at least one selected version of the first signal. The method also includes generating multiple delayed versions of the second signal using at least one second delay line, and selecting at least one version of the second signal. In addition, the method includes modifying selection of the at least one version of the first signal and the at least one version of the second signal to achieve a desired output signal based on the at least one selected version of the second signal. This method could be used in various circuits, such as duty cycle correction circuits, frequency multiplier circuits, and digital multiphase oscillator circuits.

1. A method, comprising:
 generating multiple delayed versions of a first signal using at least one first delay line; 
 selecting at least one version of the first signal; 
 generating a second signal based on the first signal and the at least one selected version of the first signal; 
 generating multiple delayed versions of the second signal using at least one second delay line; 
 selecting at least one version of the second signal; and 
 modifying selection of the at least one version of the first signal and the at least one version of the second signal to achieve a desired output signal, wherein the modifying is based on the at least one selected version of the second signal. 
 
   
   
     2. The method of  claim 1 , wherein:
 the at least one first delay line comprises a first coarse delay line; 
 the at least one second delay line comprises a second coarse delay line; 
 selecting the at least one version of the first signal comprises using a first multiplexor capable of receiving the delayed versions of the first signal from the first coarse delay line; and 
 selecting the at least one version of the second signal comprises using (i) a second multiplexor capable of receiving the delayed versions of the second signal from the second coarse delay line and (ii) a third multiplexor capable of receiving some of the delayed versions of the second signal from the second coarse delay line and the second signal. 
 
   
   
     3. The method of  claim 1 , wherein:
 the at least one first delay line comprises (i) a first offset delay line and (ii) a first fine delay line coupled to the first offset delay line; 
 the at least one second delay line comprises (i) a second offset delay line and (ii) a second fine delay line coupled to the second offset delay line; 
 selecting the at least one version of the first signal comprises using a first multiplexor capable of receiving the delayed versions of the first signal from the first fine delay line; and 
 selecting the at least one version of the second signal comprises using a second multiplexor capable of receiving the delayed versions of the second signal from the second fine delay line. 
 
   
   
     4. The method of  claim 3 , wherein selecting the at least one version of the second signal further comprises using a third multiplexor capable of receiving some of the delayed versions of the second signal from the second fine delay line and an output of the second offset delay line. 
   
   
     5. The method of  claim 1 , wherein:
 the at least one first delay line comprises (i) a first coarse delay line and (ii) a first fine delay line; 
 the at least one second delay line comprises (i) a second coarse delay line and (ii) a second fine delay line; 
 selecting the at least one version of the first signal comprises using (i) a first multiplexor coupled to the first coarse delay line, an output of the first multiplexor coupled to the first fine delay line, and (ii) a second multiplexor coupled to the first fine delay line and capable of providing one version of the first signal; and 
 selecting the at least one version of the second signal comprises using (i) a third multiplexor coupled to the second coarse delay line, an output of the third multiplexor coupled to the second fine delay line, and (ii) a fourth multiplexor coupled to the second fine delay line and capable of providing one version of the second signal. 
 
   
   
     6. The method of  claim 5 , wherein the modifying is based on the at least one selected version of the first signal and the at least one selected version of the second signal. 
   
   
     7. The method of  claim 6 , wherein:
 selecting the at least one version of the first signal further comprises using (iii) a fifth multiplexor coupled to the first fine delay line and to the output of the first multiplexor, the fifth multiplexor capable of providing another version of the first signal; 
 selecting the at least one version of the second signal further comprises using (iii) a sixth multiplexor coupled to the second fine delay line and to the output of the third multiplexor, the sixth multiplexor capable of providing another version of the second signal; and 
 both provided versions of the first signal are used to control the first and third multiplexors, and both provided versions of the second signal are used to control the second, fourth, fifth, and sixth multiplexors. 
 
   
   
     8. The method of  claim 1 , wherein:
 the at least one first delay line comprises a first coarse delay line; 
 the at least one second delay line comprises a plurality of second coarse delay lines; 
 selecting the at least one version of the first signal comprises using a first multiplexor coupled to the first coarse delay line; and 
 selecting the at least one version of the second signal comprises using (i) a plurality of second multiplexors, each second coarse delay line associated with one of the second multiplexors, and (ii) a third multiplexor coupled to a last of the second coarse delay lines. 
 
   
   
     9. The method of  claim 8 , further comprising inverting an input to each of the second coarse delay lines. 
   
   
     10. The method of  claim 8 , further comprising:
 using outputs from at least some of the multiplexors to generate the output signal. 
 
   
   
     11. The method of  claim 1 , wherein:
 modifying the selection of the versions of the first and second signals comprises modifying one or more outputs of one or more counters; and 
 selecting the at least one version of the first signal and selecting the at least one version of the second signal comprise selecting the versions of the first and second signals based on the one or more outputs of the one or more counters. 
 
   
   
     12. The method of  claim 11 , wherein modifying the one or more outputs of the one or more counters comprises incrementing and decrementing a counter value of a counter based on:
 one version of the second signal; and 
 one of: a different version of the second signal and the second signal. 
 
   
   
     13. The method of  claim 11 , wherein modifying the one or more outputs of the one or more counters comprises dividing a counter value of a counter based on one version of the second signal. 
   
   
     14. The method of  claim 11 , wherein:
 the one or more counters comprise a plurality of counters; and 
 further comprising preventing one of the counters from altering its output while another of the counters is altering its output. 
 
   
   
     15. The method of  claim 1 , wherein at least one of:
 the desired output signal has a duty cycle of approximately fifty percent; and 
 the desired output signal comprises a frequency multiple of the first signal. 
 
   
   
     16. The method of  claim 1 , wherein the desired output signal comprises the second signal. 
   
   
     17. A circuit, comprising:
 at least one first delay line capable of generating multiple delayed versions of a first signal; 
 first selection circuitry capable of selecting at least one version of the first signal; 
 circuitry capable of generating a second signal based on the first signal and the at least one selected version of the first signal; 
 at least one second delay line capable of generating multiple delayed versions of the second signal; 
 second selection circuitry capable of selecting at least one version of the second signal; and 
 control circuitry capable of controlling, based on the at least one selected version of the second signal, the first selection circuitry and the second selection circuitry to achieve a desired output signal. 
 
   
   
     18. The circuit of  claim 17 , wherein:
 the at least one first delay line comprises a first coarse delay line; 
 the at least one second delay line comprises a second coarse delay line; 
 the first selection circuitry comprises a first multiplexor capable of receiving the delayed versions of the first signal from the first coarse delay line; and 
 the second selection circuitry comprises (i) a second multiplexor capable of receiving the delayed versions of the second signal from the second coarse delay line and (ii) a third multiplexor capable of receiving some of the delayed versions of the second signal from the second coarse delay line and the second signal. 
 
   
   
     19. The circuit of  claim 17 , wherein:
 the at least one first delay line comprises (i) a first offset delay line and (ii) a first fine delay line coupled to the first offset delay line; 
 the at least one second delay line comprises (i) a second offset delay line and (ii) a second fine delay line coupled to the second offset delay line; 
 the first selection circuitry comprises a first multiplexor capable of receiving the delayed versions of the first signal from the first fine delay line; and 
 the second selection circuitry comprises a second multiplexor capable of receiving the delayed versions of the second signal from the second fine delay line. 
 
   
   
     20. The circuit of  claim 19 , wherein the second selection circuitry further comprises a third multiplexor capable of receiving some of the delayed versions of the second signal from the second fine delay line and an output of the second offset delay line. 
   
   
     21. The circuit of  claim 17 , wherein:
 the at least one first delay line comprises (i) a first coarse delay line and (ii) a first fine delay line; 
 the at least one second delay line comprises (i) a second coarse delay line and (ii) a second fine delay line; 
 the first selection circuitry comprises (i) a first multiplexor coupled to the first coarse delay line, an output of the first multiplexor coupled to the first fine delay line, and (ii) a second multiplexor coupled to the first fine delay line and capable of providing one version of the first signal; and 
 the second selection circuitry comprises (i) a third multiplexor coupled to the second coarse delay line, an output of the third multiplexor coupled to the second fine delay line, and (ii) a fourth multiplexor coupled to the second fine delay line and capable of providing one version of the second signal. 
 
   
   
     22. The circuit of  claim 21 , wherein:
 the first selection circuitry further comprises (iii) a fifth multiplexor coupled to the first fine delay line and to the output of the first multiplexor, the fifth multiplexor capable of providing another version of the first signal; and 
 the second selection circuitry further comprises (iii) a sixth multiplexor coupled to the second fine delay line and to the output of the third multiplexor, the sixth multiplexor capable of providing another version of the second signal. 
 
   
   
     23. The circuit of  claim 17 , wherein:
 the at least one first delay line comprises a first coarse delay line; 
 the at least one second delay line comprises a plurality of second coarse delay lines; 
 the first selection circuitry comprises a first multiplexor coupled to the first coarse delay line; and 
 the second selection circuitry comprises (i) a plurality of second multiplexors, each second coarse delay line associated with one of the second multiplexors, and (ii) a third multiplexor coupled to a last of the second coarse delay lines. 
 
   
   
     24. The circuit of  claim 23 , further comprising a plurality of inverters capable of inverting an input to each of the second coarse delay lines. 
   
   
     25. The circuit of  claim 23 , further comprising circuitry capable of using outputs from at least some of the multiplexors to generate the output signal. 
   
   
     26. The circuit of  claim 17 , wherein the circuitry capable of generating the second signal comprises an XOR gate. 
   
   
     27. The circuit of  claim 17 , wherein:
 the first selection circuitry and the second selection circuitry comprise a plurality of multiplexors; and 
 the control circuitry comprises one or more counters, wherein one or more outputs from the one or more counters are capable of controlling the plurality of multiplexors. 
 
   
   
     28. The circuit of  claim 27 , wherein at least one of the one or more counters is capable of incrementing and decrementing a counter value based on:
 one version of the second signal; and 
 one of: a different version of the second signal and the second signal. 
 
   
   
     29. The circuit of  claim 27 , wherein at least one of the one or more counters is capable of dividing a counter value based on one version of the second signal. 
   
   
     30. The circuit of  claim 27 , wherein:
 the one or more counters comprise a plurality of counters; and 
 further comprising at least one finite state machine capable of preventing one of the counters from altering its output while another of the counters is altering its output. 
 
   
   
     31. The circuit of  claim 17 , wherein the desired output signal comprises one of: the second signal and an output signal based on the second signal. 
   
   
     32. A digital multiphase oscillator, comprising:
 a phase generator capable of generating a plurality of out-of-phase signals; 
 a control signal generator capable of generating a plurality of control signals for the phase generator; and 
 a pulse generator capable of generating a plurality of clock signals for the control signal generator, the pulse generator comprising:
 at least one first delay line capable of generating multiple delayed versions of a first signal; 
 first selection circuitry capable of selecting at least one version of the first signal; 
 circuitry capable of generating a second signal based on the first signal and the at least one selected version of the first signal; 
 at least one second delay line capable of generating multiple delayed versions of the second signal; 
 second selection circuitry capable of selecting at least one version of the second signal; and 
 control circuitry capable of controlling, based on the at least one selected version of the second signal, the first selection circuitry and the second selection circuitry; 
 
 wherein the second signal and one or more of the at least one selected version of the second signal comprise the clock signals. 
 
   
   
     33. The digital multiphase oscillator of  claim 32 , wherein:
 the at least one first delay line comprises a first coarse delay line; 
 the at least one second delay line comprises a plurality of second coarse delay lines; 
 the first selection circuitry comprises a first multiplexor coupled to the first coarse delay line; and 
 the second selection circuitry comprises (i) a plurality of second multiplexors, each second coarse delay line associated with one of the second multiplexors, and (ii) a third multiplexor coupled to a last of the second coarse delay lines; 
 wherein the second signal and outputs of the second multiplexors comprise the clock signals.